Adaptive error correction device for a laser scanner

A laser scanner comprising:

• a laser for generating a laser beam;
• an acoustooptic modulator for modulating said laser beam;
• a photosensitive drum;
• a multiple facet mirror receiving said laser beam and sweeping said laser beam across said photosensitive drum with each facet upon rotation of said spinner and said drum;
• photodetector means positioned to receive said laser beam immediately prior to said sweeping across said photosensitive drum, said photodetector means having a mask to block part of said laser beam to generate a stepped voltage output upon receiving said laser beam;
• comparator means for generating a start-of-scan signal for each facet upon receiving said stepped output voltage;
• first delay means connected to said comparator means to give an amplitude correction signal after a first predetermined time period from said start-of-scan signal;
• second delay means connected to said comparator means to give a frequency correction signal after a second predetermined time period from said start-of-scan signal;
• memory means for storing previous amplitude and frequency modulation for said acoustooptic modulator for each facet of said mirror;
• correction means receiving said amplitude correction signal and said frequency correction signal to adjust said previous amplitude and frequency modulation of said acoustooptic modulator for intensity correction and facet-to-axis correction of said laser beam, respectively, and store said adjusted amplitude and frequency modulation in said memory means, said adjusted amplitude and frequency modulation operating said acoustooptic modulator.